In previous studies we demonstrated that one of the initial signals induced by the binding of Epidermal Growth Factor (EGF) to membrane containing specific EGF receptors was the stimulation of protein phosphorylation. To test the hypothesis that EGF stimulated membrane phosphorylation is one of the initial growth regulatoy signals induced in EGF sensitive cells we have chosen to analyze the phosphorylation in the human epidermoid cancer cell line, A-431. In this model system we propose to (1) characterize the membrane associated, phosphorylated compounds by gel electrophoresis methods using combinations of membrane labeling, digestion and extraction methods; (2) to characterize the nature and specifity of the EGF stimulated reaction in the isolated A-431 membranes and (3) to study the involvement of specific membrane components of the A-431 cells in the initial events occurring after binding of EGF to whole cells and isolated membranes. The EGF binding and EGF stimulated protein kinase has been solubilized with nonionic detergents and purified by affinity chromatography from these A-431 membranes (Cohen, Carpenter, King, JBC 255, 4834, 1980). Studies to characterize the nature of the EGF related components are being continued using the A-431 membranes.